The name Triassic comes from Germany where it was originally named the Trias in 1834 by Friedrich August Von Alberti (1795-1878) because it is represented by a three-part division of rock types in Germany. The three distinctive formations from the bottom up are the Bunter, the Muschelkalk, and the Keuper. These rock units are often equated to the Early, Middle, and Late Triassic Epoch designations, respectively, although these rock types are local German formations and should not be applied globally.
In many ways, the Triassic was a time of transition. This period followed the largest extinction event in the history of life where approximately 95% of all species and about 60% of the genera died out. The cause of the Permian extinction is not completely understood but it is theorized that it might have been global cooling, volcanic eruptions, or a decrease in the continental shelf area during the formation of Pangaea. It was a time when the survivors of the extinction spread and re-colonized, new groups of life appeared and then died out, and new life forms rose, flourished, and went on to dominate the Mesozoic world.
The Triassic Period came to a close with another mass extinction around 206 million years ago which may have been caused by global cooling and/or an asteroid impact. This extinction eliminated 35 percent of all animal families including the labyrinthodont amphibians, conodonts, marine reptiles, and synapsids.
Tectonics and Paleoclimate
At the beginning of the Triassic period, the land masses of the world were still bound together into the vast super continent known as “Pangaea”. Pangaea began to break apart in the mid-Triassic, forming Gondwana (South America, Africa, India, Antarctica, and Australia) in the south and Laurasia (North America and Eurasia) in the north. The movement of the two resulting super continents was caused by sea floor spreading at the midocean ridge lying at the bottom of the Tethys Sea, the body of water between Gondwana and Laurasia. While Pangaea was breaking apart, mountains were forming on the west coast of North America by subduction of the ocean plates beneath the continental plates.
Throughout the Middle to Late Triassic, mountain forming continued along the coast extending from Alaska to Chile. As mountains were forming on the Americas, North Africa was being split from Europe by the spreading rift. This division of the continents advanced further westward, eventually splitting eastern North America from North Africa.
The climate of the Triassic era was influenced by Pangaea’s centralized position straddling the equator and the geologic activity associated with its breakup. Generally speaking, the continents were of high elevation compared to sea level and the sea level did not change drastically during the period. Due to the low sea level, flooding of the continents to form shallow seas did not occur. Much of the inland area was isolated from the cooling and moist effects of the ocean. The result was a globally arid and dry climate, though regions near the coast most likely experienced seasonal monsoons. There were no polar ice caps, and the temperature gradient in the north-south direction is assumed to have been more gradual than present day. The sea level rose as the rift grew between North Africa and southern Europe, resulting in the flooding of Central and South Europe; the climates of terrestrial Europe were hot and dry, as in the Permian. Overall, it appears that the climate included both arid dune environments and moist river and lake habitats with gymnosperm forests.
The flora during the Triassic Period varied on the newly forming land masses Gondwana and Laurasia. On Gondwana, the Permian Glossopteris flora disappears and is replaced by the seed-fern Dicrodium which becomes the dominate plant form inhabiting most regions from heath and broad-leafed forest to dry woodlands. Voltziacean and primitive podocarpaceous conifers, peltaspermaceous seed ferns, cycads, and ginkgos also make their appearance. On Laurasian, the flora is dominated by primitive conifers (e.g., Voltziaceae and Lebachiaceae) accompanied by cycads, cycadeoids, bennettitales, ginkgos, sphenopsids, and ground/tree ferns.
In the aquatic environments, fusilinid foraminifers, lacy bryozoans, rugose corals, and trilobites that had characterized the late Paleozoic had all disappeared by the Triassic Period. Bivalves, ammonoids, and brachiopods recovered from the Permian extinction and became abundant during the Triassic. These creatures were joined by new groups of coloeids (squid-like animals) including the Belemnites. Most modern groups of invertebrates also appeared during the Triassic including echinoderms (starfish, sea urchins and their relatives) as well as scleractinian corals. The rivers, ponds and lakes were populated by large temnospondyls such as Capitosauria and Mastodonsaurus as well as the Ceratodan lungfish. The seas contained an unprecedented diversity of marine reptiles including the dolphin-like ichthyosaurs, the lizard-like pachypleurosaurs and thalattosaurs, the long-necked seal-like nothosaurs, walrus-like placodonts, the turtle-like henodonts, and the long-necked Pistosaurs.
In the air, the pterosaurs ("flying reptiles") first appeared and amongst the trees and low lying vegetation, the Pseudosuchia, possible ancestor of Archaeopteryx, made its appearance.
On land, a variety of important terrestrial life forms evolved including salamanders, turtles, crocodiles, and lizards (including sphenodonts & snakes). Insects began to undergo complete metamorphosis from larva through pupa to adult. The first proto-dinosaurs evolved including the Herrerasaurus, Coelophysis, Staurikosaurus, Ischisaurus, and Chindesaurus. Finally, the first true mammals such as Eozostrodon, Megazostrodon, Erythrotherium Dromatherium and Microconodon made their way onto the Triassic landscape.
Meteorite Impacts on Earth
I included a list of meteorite impacts relevant to this time period as a point of reference since many of the explanations for mass extinctions throughout Earth’s history include meteorite impact(s) as a possible cause. The meteorite impact information below was obtained from the ‘Earth Impact Database’ maintained by the Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada ( www.passc.net/EarthImpactDatabase).